The invention pertains to sewing machines and, more especially, to a device for feeding tapes, elastic strips or the like (hereinafter referred to as "tapes") for attachment to a workpiece in timed relation to the latter's advance along the machine's work surface during the sewing cycle.
The intended function of the device is that of controlling the feed of tape to the workpiece in timed sequence to the operating speed of a sewing machine and, depending on the requirements thereof, the tapes can be fed in an amount equal to or less than the amount of advance of the workpiece by the machine's conventional transport mechanism. The supply of tape is equal to the amount of advance of the workpiece when it is intended to be attached thereto without pre-tensioning and in a lesser amount if it is intended to pleat the workpiece during the stitching operation.
The device includes a motor member with control and command elements associated therewith whereby the tape feed rollers can be synchronized with the operating speed of the machine and for effecting necessary changes thereto to compensate for any variation in the operating speeds of the machine.
If the machine could be operated continuously at a constant speed, the device, according to the invention, would not be necessary; however, as the operating speed is never constant due to the ever present inertia of mechanical elements, and, with the lack of such a device, there is no means for effecting automatic adjustment of the tape feed to compensate for changes in the machine's operating speed. Such a condition creates an undesirable tensioning buildup during machine acceleration and with an excessive amount of tape being present during deceleration.
In known sewing machines these discrepancies due to inertia are quite obvious for when the machine is accelerating the tape becomes tensioned to a greater degree and during deceleration the tape becomes slacker due to a greater amount being fed through the feed rollers in comparison to the amount of advance of the workpiece by the transport mechanism.
Although these conditions are quite obvious, the known machines are not equipped with devices for correcting such conditions. As a result of this sort of inertia, with each variation of the machine's operating speed, there is no synchronization between the supply to the tape feed rollers and the mechanism for advancing the workpiece and, as the machine continues to operate, these discrepancies become more pronounced by being added to one another.
An object of the invention is to provide a device which is capable of detecting a discrepancy of the type described supra and immediately take the necessary steps to correct and compensate for the discrepancy.